This invention is generally directed to processes for the preparation of silica containing charge enhancing additives. More specifically, the present invention is directed to processes for the preparation of silica containing charge enhancing additives by the hydrolysis/condensation of tetraalkoxysilanes in the presence of charge enhancing additives such as distearyl dimethyl methylsulfate. With the process of the present invention, there is obtained in an economical, substantially one step method the preparation of charge enhancing additives sorbed on silica, particularly colloidal silica in a uniform and continuous manner. In addition, the process of the present invention enables products with particle size control and desirable surface property characteristics. In addition, with the process of the present invention there is selected an aqueous solution of readily available economical reaction components. Advantages associated with the one step economical processes of the present invention include obtaining a uniform distribution of the charge additive on the silica; minimization of the hazards relating to the processing of fine powders; increased control of the chemical composition and the average diameter particle size of the resulting charge additive; and improved electrical performance and flow characteristics, especially when the charge additive products are selected for toner compositions. The treated silica charge enhancing additive products obtained with the process of the present invention can be selected as external additives for toner compositions, including magnetic, black and colored toner compositions. Developer compositions with the modified charge enhancing additives of the present invention are useful for enabling the development of electrostatic latent images including color images. More specifically, toner compositions with the aforementioned modified charge enhancing additives are particularly useful in electrophotographic imaging processes having incorporated therein a Viton coated fuser roll since these additives do not react substantially with Viton causing undesirable decomposition thereof which adversely effects imaging quality. Also, toner compositions with the treated additives of the present invention possess improved admix characteristics while enabling colored toner compositions with high concentrations of colorant. Additionally, the modified charge enhancing additives of the present invention are of acceptable fusing performance characteristics in that, for example, these additives have substantially no effect on fusing performance; and further, the additives of the present invention are compatible with, for example, many alternative types of fuser rolls inclusive of Viton, Teflon, fluorinated ethylene polymers, silicones, and the like.
There are disclosed in a number of prior art patents developer compositions with charge enhancing additives. Thus, for example, there are illustrated in U.S. Pat. No. 3,893,935 toner compositions with certain quaternary ammonium salts as charge enhancing additives. Further, in U.S. Pat. No. 2,986,521 reversal developer compositions comprised of toner resin particles coated with finely divided colloidal silica are illustrated. According to the disclosure of this patent, development of electrostatic latent images on negatively charged surfaces is accomplished by applying a developer composition with a positively charged triboelectric relationship in respect to the colloidal silica. Moreover, toner compositions with sulfate and sulfonate charge enhancing additives are described in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference. Also, U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, illustrates toner compositions with alkyl pyridinium halide charge enhancing additives.
Other documents disclosing toner compositions with charge control additives include U.S. Pat. Nos. 3,944,493; 4,007,293; 4,079,014 and 4,394,430. Also of interest are Japanese Patent Abstract Publications 55079-454; 57129-446; 57079-951; 57078-550; and German DE 3208635. Disclosed in the '454 abstract is a dry processable electrophotographic developer with a hard powder, such as aluminum oxide which has been previously subjected to surface treatment. The '446 document discloses an electrophotographic developer with silica fine powder as a charge control agent; while the '951 abstract illustrates a photographic developer containing a micropowder of silicate coated with alumina, and having a stable frictional charge between a developer and toner in a sleeve. In the German publication '635, there are disclosed toner particles and additive particles incorporated for the primary purpose of improving flowability. In the abstract of the aforementioned publication, there is mentioned as a charge control agent a metal complex dye; and further that hydrophobic colloidal silica can be selected as a flow additive. Additionally, chemically modified surface additives such as Aerosil have been disclosed in West German patent publication DE 3330380. Specifically, this publication is directed to alkoxyaminosilanes which are chemically reacted with free silanol groups.
Toner compositions with many of the above described charge enhancing additives, including those obtained by the process of the present invention, can be selected for the development of images formed on layered photoresponsive imaging devices comprised of photogenerating layers and transport layers, reference U.S. Pat. No. 4,265,990 the disclosure of which is totally incorporated herein by reference. These devices are charged negatively, rather than positively as is usually the situation with selenium photoreceptors, thus a toner composition which is positively charged is selected to enable toner particles to be suitably attracted to the electrostatic latent image contained on the photoreceptor surface. Thus, efforts have been devoted to obtaining developer compositions containing toner resins which are positively charged. Thus, there continues to be a need for preparation processes that will enable charge enhancing additives, especially those that will not interact with fuser rolls. Moreover, there continues to be a need for preparation processes that will provide charge control additives which are stable at high temperatures. Also, there continues to be a need for preparation processes that will permit the formation of charge enhancing additives for positively or negatively charged toner and developer compositions with rapid admix charging characteristics. Additionally, there is a need for preparation processes wherein silica based external charge control additives result, which additives in addition to being thermally stable, are substantially nontoxic. Also, there is need for colored toner compositions which contain positively or negatively charged resin particles with the silica based charge enhancing additives obtained by the process of the present invention, and wherein the resulting toner compositions have desirable toner admix charging. Specifically, there is a need for toner compositions having sorbed thereon modified charge enhancing additives as illustrated herein, which toner compositions can be negatively or positively charged depending, for example, on the carrier components selected; possess improved admix characteristics, that is the toner compositions acquire their charge in a rapid time period, less than 1 minute for example, while simultaneously possessing other improved characteristics as illustrated hereinafter, inclusive of acceptable electrical properties such as an appropriate positive or negative triboelectric charge.